Magnetostrictive oscillator



Oct. 26, 1943. E. E. TURNER, .1R

MAGNETOSTRICTIVE OSCILLATOR Filed Au. l2, 1940 2 Sheets-Sheet l INVENT OR.

' ATTO EDWIN ETURN ERJR.

Oct. 26, 1943. E. E. TURNER, JR 2,332,541

MAGNETOSTRICTIVE OSCILLATOR Filed Aug. l2, 1940 2 Sheets-S1169?r 2 www R IWIIII\!IIII lllllllll INVENTOR. EDWIN E. TURNER, JR.

Patented Oct. 26, 1943 MAGNETOSTRICTIVE OSCILLATOR Edwin E. Turner, Jr., West Roxbury, Mass., as-

signor to Submarine Signal Company, Boston, Mass., a corporation of Maine Application August 12, 1940, serial No. 352,261

4 Claims.

The present invention relates to underwater compressional wave senders and receivers and particularly to such senders and receivers of the laminated magnetostrictive type. Still more particularly the present invention relates to compressional wave transmitters and receivers and reilectors therefor especially adapted to use in rial such as nickel which is relatively expensive.

It has also been proposed to mount such one-half wave length vibrators in reflectors to produce a downwardly directive beam of compressional waves. In this case the block of laminations is usually mounted to vibrate in the horizontal plane, so that compressional waves from the ends of the laminations travel horizontally to the refiector by which they are directed downwards. The beam pattern of such a device is considerably distorted from the beam pattern produced by a plane piston vibrating with uniform amplitude over its surface and having a size substantially equal to the area of the mouth of the reflector because of the space occupied by the stack of laminations, from which space there is no downward radiation.

It is an object of the present invention to provide a laminated magnetostrictive oscillator having a minimum width dimension for a specified frequency. A further object of the invention is to provide a laminated magnetostrictive oscillator in which each of the laminations contains a minimum amount of magnetostrictive material. A still further object of the present invention is to provide a laminated magnetostrictive oscillator and reflector assembly particularly adapted for mounting on the inside skin of a ship for depth sounding purposes and having an improved beam pattern.

The above and other objects of the invention will best be understood from the following description taken in connection with the accompanying drawings in which Fig. l shows a midsection of the oscillator and reflector; Fig. 2 is another sectional view of the oscillator and reflector taken along the line II-Il in Fig. l; Fig. 3

. is a plan view of one-half of one lamination; Fig.

4 isa reduced perspective view of a portion of the stack of laminations and Fig. 5 shows a horizontal section of the apparatus taken on the plane V-V of Figs. 1 and 2.

As shown by the drawings the oscillator, which can be used as both transmitter and receiver of compressional waves, is made up of a stack I of laminations supported by a strap 2 and bolts 3 screwed into the cover plate# of a housing having side walls 5, 6, 'l and 8, the last two forming reflectors for the wave energy produced by the laminations I. The cover plate 4 is secured to the side walls ofthe housing by means of bolts 9 threaded into ears I0 formed integrally with the walls l and 8. At the bottom of the housing, which is open, there is provided a rubber gasket II so that the entire unit can be held against the'inner skin of a ship by suitable means and thereby form an enclosed chamber which can be lled with water or other compressional wave conducting material by means of the filling plugs I2. The inner surfaces of the walls 5 to 8 are lined with suitable compressional wave insulating material I3 `such as cellular sponge rubber. This is held in place on walls 5 and 6 by metal strips I4 and screws I5. On walls I and 8 a thin metal sheet 21 covers the rubber and serves as a wave reflecting material. This is secured to the walls of the housing by means of screws 28.

'I'he individual laminations are rectangular in Shape, a plan view of one-half a lamination being shown in Fig. 3. In the center of each lamination is a series of elongated parallel apertures I6 adapted to receive the windings forming the exciting coils which are wound in such a way that when excited with alternating current of the proper frequency, the laminations will expand and contract magnetostrictively in the direction of the double-headed arrow Il. The dimension Il is, however, not one half a wave length'as heretofore used in the art, but is considerably less than one half a wave length of compressional waves in the magnetostrictive material of the laminations at the resonant frequency. I attain this result byplacing the aper- --tures i6 so close together that the material I8 between the apertures has a very small mass compared to its stiiness. The solid material I9 on each side of the row of apertures has, however, considerable mass. The vibrating system considered in the direction of the arrow Il, therev fore, comprises two mass elements I8 connected by a plurality of parallel elastic elements I8, the mass and elasticity of the system being substantially separated. In other words, substantially all the vibrating mass is concentrated in the portions I9 while substantially all the elasticity of the system is concentrated in the elements I8. The width of the solid elements I9 at each side of the row of apertures I6 is adjusted so that the unit will have a resonant frequency of vibration in the direction of the arrow I'I equal to the desired signaling frequency. The width of the elements I9, as indicated by the arrows 24, must, however, be less than one eighth of a wave length of compressional waves of the resonant frequency in the material, so that there will be no wave motion in these mass elements, but they will vibrate as a whole, al1 the elasticity of the system being in the elements I8.

The width of the apertures I6 considered in the direction perpendicular to the arrow II in Fig. 3 is preferably made just large enough to accommodate the coil windings 26 necessary to produce the desired flux density. I prefer to use a relatively heavy wire for the windings 26, the wire being threaded down through one aperture, up through the next, down through the next, and so on, then back in a similar manner until the apertures are entirely filled, care being taken that the turns around each element I8 are all in the same direction, but those around adjacent elements are in the opposite direction. The magnetic flux then flows in opposite directions through adjacent elements I8, the flux path being closed by the elements I9. In my preferred ccnstruction the wires are pulled tightly through the apertures I6 whereby they serve to hold the stack of laminations together, no other clamping means being required.

As before mentioned, the block of laminations may be supported by a metallic strap 2 passing around the ends and bottom of the block, rubber strips 25 being used to fill the space not occupied by the windings 26 and to insulate the ends of the laminations acoustically from the supporting strap and the cover of the housing.

By this means I am able to reduce the width of the laminations in the direction of vibration to a minimum for a vibrator of any given frequency, the frequency being proportional to the square root of the ratio of the stiffness to the mass. Not only does my construction make possible a narrow vibrating unit, but also it increases the eficiency of operation since the active magnetrostrictive material is operated at a high ux density. Moreover, the amount of magnetostrictive material required for a vibrator of given frequency and power output is considerably reduced.-

When the stack of laminations is mounted within the reflector housing and the latter is filled with a suitable wave-conducting liquid, the vibrations from the laminated block I will travel through the liquid in a horizontal direction to one of the reecting walls I or 8 of the housing as indicated, for example, by the lines 20 or 2I. These walls of the housing are substantially plane surfaces arranged at 45 to the plane of the laminations. After reflection from the walls of the housing, the sound will travel downwards as indicated, for example, by the lines 22 or 23. There will thus be compressional wave energy transmitted downwards toward the open end of the housing whence it can pass through the ships skin and into the outer water. There will, however, be no downward radiation produced directly beneath the laminated unit I. This space l in which there is no radiation is. however, by

'the present invention reduced to a minimum,

whereby an improved beam pattern results.

The stack of laminations is thus in the form of a prism having a length which is large compared to the wave length of compressional waves in the water medium at the signaling frequency, while its width is considerably less than a wave length in water. The stack of laminations is made high enough so that the bottom edges of the 45 reflectors I and 8 will be spaced apart by a distance which is large compared to a wave length of waves of the signaling frequency in water.

Withoutglimitation, but merely by way of example, the following dimensions can be used in constructing a compressional wave transmitter and receiver in accordance with the present invention: For a transmitter and receiver for use at 16.5 kilocycles the individual laminations may be made of 0.01 inch thick heat-treated nickel sheet 2.25 inches by 10.0 inches in size with apertures shaped as shown in Fig. 3 and 0.192 inch in narrow dimension and 0.75 inch in long dimension spaced 0.022 inch apart. The width of the members I9, i. e., the dimension 24 in Fig. 3 may be 0.75 inch. A stack of such laminations seven inches high with two effective coil turns around each element I8 excited to produce in the elements I8 an effective alternating magnetic ux density of maximum value of 50 gauss may be mounted in the trapezoidal, rectangular-mouthed reflector having a ,bottom opening approximately 14 by. 16.25 inches.

In order that the webs I8 will act only as elastic members, the total mass of the webs I8 should, as in the above example, be kept small compared to the mass of each of the end members I9; preferably the mass of the webs should not exceed one fifth of the massof the end members. Stated 1n another way, the width of the webs, measured between adjacent apertures should be of the order of magnitude of their thickness, that is not greater than ten times the thickness of the individual laminae. Also, in order that the members I9 shall act only as masses substantially without wave motion, the apertures should be limited in width so that the portion of elements I9 included between the center lines of adjacent apertures shall at all events not be longer than one eighth wave length of compressional waves in the material at the resonant frequency, and better not more than one sixteenth of a wave length. I prefer, however, to keep the center lines of adjacent apertures even much closer together than one sixteenth of a wave length, las in the above example in which this spacing is less than one one-hundredth of the wave length, so that wave motion in the members I9 is substantially excluded.

Having now described my invention, I claim:

1. In combination, means for producing a beam of compressional waves above the limit of audibility in a liquid medium comprising a reflector having an axis extending normal to the opening thereof lled on the inside with said liquid medium, said opening having linear dimensions large compared to the wave length of the compressional wave in the liquid medium, a magnetostrictive compressional wave producing means mounted substantially wholly within said reflector, said magnetostrictive means having parallel radiating surfaces parallel to the axis of the refiector and having a plurality of combined resonant elements extending normally be= tween said parallel surfaces, said surfaces being spaced apart from one another substantially less than the normal half wave length resonance of a uniform piece of the same material forming said magnetostrictive element, whereby the reflected energy is delivered substantially uniformly from the reflector at its opening.

2. In combination means for producing a beam of compressional waves above the limit of audibility in a liquid medium comprising a reflector having an axis extending normal to the opening thereof filled on the inside with said liquid medium, said opening having linear dimensions large compared to the wave length of the compressional wave in the liquid medium, a magnetostrictive compressional wave producing means mounted substantially Wholly within said reector, said magnetostrictive means comprising mass elements having parallel radiating surfaces parallel to the axis of said reflector, said mass elements being joined by magnetostrictive elastic means having substantially no mass and forming with said mass elements resonant vibrators, the distance between said surfaces being spaced apart substantially less than the normal half wave length resonance of a uniform piece of the same material forming said magnetostrictive element whereby the reflected energy is delivered substantially uniformlyfrom the reiiector at its opening.

3. In combination, means for producing a beam of compressional waves above the limit of audibility in a liquid medium comprising a reector having an axis extending normal to the opening thereof filled on the inside with said liquid medium, said opening having linear dimensions large compared to the wave length of the compressional wave in the liquid medium, a magnetostrictive compressional wave producing means mounted substantially wholly within said reflector, said magnetostrictive means comprising a plurality of thin nat laminations having a plurality of parallel uniform perforations positioned longitudinally in the width dimension of said laminations and providing sections of material between perforations substantially narrower than the width of said perforations whereby when said laminations are stacked and aligned together,

a vibratory structure is formed having substantial end mass joined by elastic sections having substantially no mass, whereby a structure is produced having a half wave length resonance that is substantially smaller in longitudinal dimensions than a uniform piece of the same material and electric conducting means threading said perforations for magnetostrictively energizing sections of the material therebetween, said magnetostrictive 'means having radiating surfaces parallel to the axis of the reflector whereby the reflected energy reflected from the walls of the reflector is delivered substantially uniformly from the reector at its opening.

4. In combination, means for producing a beam of compressional waves above the limit of audibility in a liquid medium comprising a reflector having an axis extending normal to the opening thereof fllled on the inside with said liquid medium, acoustic insulating means lining the inside of said reflector at the' sides thereof, said reflector having a back portion substantially rectangular in Shape and said opening having linear dimensions large compared to thewave length of the compressional wave in the liquid medium, a magnetostrictive compressional wave producing means having an elongated rectangular shape at one endand positioned with said end at the top of said reflector and extending normally parallel with the axis of said reflector, said magnetostrictive compressional Wave producing means having parallel radiating surfaces parallel to the axis of the reflector and having a plurality of combined resonant elements lextending normally between said parallel surfaces, said surfaces being spaced apart from one another substantially less than the normal half Wave length resonance of a uniform piece of the same material forming said magnetostrictive element whereby the reected energy is'delivered substantially uniformly from the reector at its opening.

EDWIN E. TURNER. JR. 

